Hydrogen is used as a fuel in many applications today, including in fuel cells producing electric power. Fuel cells have also been proposed for use in electrical vehicular power plants to replace internal combustion engines. With the increased use of hydrogen as a fuel source, better methods of producing hydrogen gas are needed.
A common way to produce hydrogen gas is by electrolysis of water. In addition to producing hydrogen, electrolysis of water also produces oxygen. The generation of hydrogen and oxygen by electrolysis of water is performed in an electrolyzer. An electrolyzer is comprised of a plurality of cells that each have an anode side with an anode electrode and a cathode side with a cathode electrode. The anode and cathode electrodes are separated by a solid polymer electrolyte. A load or voltage (electrical potential) is applied across the anode and cathode electrodes while water is supplied to the anode side. Oxygen is generated on the anode side and excess water supplied to the anode side carries the oxygen and heat generated away from the cell. Hydrogen ions along with a small amount of the water are driven through the membrane by the electrical potential and, with the addition of electrons from the cathode, form hydrogen gas on the cathode side. The hydrogen gas and the protonic water are ported out of the cathode side of the cell. A plurality of such cells are stacked adjacent one another to form an electrolyzer capable of producing both hydrogen and oxygen gas with the addition of water and electrical potential.
Because the gases produced through water electrolysis are very pure and typically do not require additional processing, it is advantageous to match as closely as possible electrolysis pressure with that required for further processing or storage. Hydrogen, being a light gas, is preferably stored at high pressures (5,000–10,000+ psi). These high pressures provide for economical storage of the hydrogen gas. Oxygen, likewise, is also preferably stored at high pressures. While production of hydrogen or oxygen at these higher pressures is desirable, a limitation of electrolyzers has been the inability to produce hydrogen or oxygen gas at these elevated or high pressures. The limitation on the pressure at which an electrolyzer can produce hydrogen or oxygen gas has been due to the structural limitations of the individual cells. That is, the structural configuration of the individual cells limit the magnitude of the pressure differential that can exist between the anode and cathode sides without the membrane failing or rupturing. To overcome these limitations, the electrolyzer was enclosed within a pressure vessel that was then pressurized with a blanket of inert gas (nitrogen). The pressurized nitrogen was provided to both the anode and cathode sides of the electrolyzer so that the electrolyzer could be operated at a higher overall pressure while maintaining a pressure differential between the anode and cathode sides of a magnitude that does not rupture or cause premature failure of the membrane. The use of a pressurized inert gas, however, lowered the efficiency of the electrolyzer due to the requirement to compress the nitrogen gas to the desired pressures. That is, specialized mechanical devices are necessary to compress the nitrogen to these elevated pressures and requires additional energy input to accomplish the compression. The efficiency of compressing nitrogen, even though heavier than hydrogen, and the complex controls necessary to accomplish this, reduce the overall efficiency of producing hydrogen and oxygen with the electrolyzer. In order to limit the necessity of utilizing pressurized gas to pressurize the anode and cathode sides of the electrolyzer, improvements were made on the inherent pressure capabilities of the electrolyzer itself. The improvements were made to the membrane support structure that is provided in each of these cells and which allow the cells to withstand, without damage, higher differential pressures than were previously possible. Current membrane support structures in electrolyzers allow pressure differentials between the anode and cathode sides of the electrolyzer of about 2,000 psi.
Thus, current electrolyzers are capable of producing hydrogen or oxygen gas at about 2,000 psi without the use of an inert gas to increase the pressure in the anode and cathode sides of the electrolyzer. By enclosing the electrolyzer within a pressure vessel pressurized by an inert gas that is supplied to both the anode and cathode sides of the electrolyzer, production of oxygen or hydrogen at pressures higher than 2,000 psi is possible. However, as stated above, the use of an inert gas to pressurize the anode and cathode sides of the fuel cells reduces the overall efficiency of the electrolyzer.
Accordingly, it is desirable to provide a method and apparatus to produce hydrogen or oxygen gas in an electrolyzer at high pressures (5,000–10,000+ psi) in a more efficient and economical manner. To increase the efficiency, it is desirable to avoid the necessity of compressing an inert gas to pressurize a pressure vessel within which the electrolyzer is positioned.